ISO 25178 Surface Parameters for Injection Moulding Optical Components
ISO 25178 areal parameters define 3D optical surface texture to control stray light and guide injection moulding process windows for precision lenses.
L-Filter Cutoff
Meaning
A filtering threshold in surface metrology establishes the maximum wavelength allowed to contribute to a measurement of roughness. The l-filter cutoff removes long-wavelength features, such as waviness and part form, that would otherwise distort the analysis of fine textures. In polymer molding, this parameter isolates the high-frequency micro-topography from the macro-geometric defects.
Wavelength Limit
Metrological isolation of surface features requires a specific cutoff wavelength. This threshold is chosen to ensure that form errors do not skew the calculated roughness values. For high-precision lenses, the l-filter cutoff defines the boundary where structural deviations of the mold cavity end and surface roughness begins.
Mold Optimization
Steel mold finishing utilizes grinding and polishing to achieve specific gloss targets. Measuring the resulting mold surface requires the l-filter cutoff to separate the toolmarks from the overall geometry. This allows the toolmaker to evaluate the micro-roughness directly, and prevents the larger part contours from inflating the measured values.
By applying a standardized cutoff value, the process secures a true reading of the surface finish.
Defect Control
Out-of-tolerance roughness leads to increased demolding forces and surface scuffing during ejection. Isolating these issues necessitates an accurate l-filter cutoff during the post-molding audit. If the cutoff is too large, the measurement misinterprets part warpage as micro-roughness, causing false rejections of conforming parts.